The answer is B, Eli's hot cocoa.
This is because if you multiply the Arjun's hot cocoa by two to compare it to Eli's, you get
Arjuns new cocoa: 40 mL for every 6 ounces
Eli's cocoa: 45 mL for every 6 ounces
Eli has 45 mL of chocolate syrup versus Arjun's 40 mL (both in 6 ounces of water).